Electromechanical resonators are very often used as input and output transducers in multiresonator bandpass mechanical filters, and, as the filter itself, in the case of a single resonator mechanical filter. These electromechanical resonators have been designed to operate in numerous types or modes of vibration. Examples are torsion, flexure and extension. The transduction mechanisms for providing these modes of vibration have utilized the piezoelectric effect, magnetostriction and variable-reluctance magnetic effects.
Electromechanical resonators operating in the torsional mode have previously been used in the input and output of mechanical filters. These electromechanical resonators of the prior art are often coupled by wires to other torsional mode resonators wherein the composite resonator wire-coupled assembly forms a bandpass mechanical filter. These previously designed electromechanical resonators have used special piezoelectric ceramic transducers that are polarized in a direction parallel to the metal plated surfaces. This type of plated ceramic is more costly than other types such as those where the plated surfaces are used to polarize the material in a direction perpendicular to those surfaces. The parallel polarization, which excites a shear wave in the ceramic, requires plating removal and two metal parts per resonator in one embodiment and two ceramic pieces and a single metal part in another embodiment. The complexity of design of these prior art torsional resonators increases the time and cost necessary to produce same. In addition, when a part is more complex to produce, the reliability is often degraded accordingly.
The electromechanical resonator described herein as our invention, uses only one ceramic transducer and one metal base part in one embodiment. Other embodiments may use other base materials such as quartz and also the resonator can be produced using more than one transducer to further enhance various characteristics of the resonator.
It is thus an object of the present invention to improve the design of torsional electromechanical resonators, lower the cost and improve the reliability.